Rate of change of momentum = impact force
(m*v-m*u)/t = F
4000*20/t = 80000 (note: v is zero as it stopped)
<span>soo, t = 1 sec</span>
The supermassive black hole "Sagittarius A*" at the center, which exerts an enormous gravitational force on the surrounding material. This accelerates the material to relativistic speeds (0.2c) as per regular newtonian mechanics combined with the laws of special relativity.
Source: Astrophysicist